This invention relates to a semiconductor device comprising a field effect device having a gate structure provided within a trench.
In particular, this invention relates to a semiconductor device comprising a semiconductor body comprising a field effect device wherein the semiconductor body has source and drain regions spaced apart by a body region and both meeting a surface of the semiconductor body, the field effect device having a gate structure provided within a trench for controlling a conduction channel in a conduction channel accommodation portion of the body region extending along at least the side walls of the trench and between the source and drain regions.
U.S. Pat. No. 4,835,584 describes such a trench transistor in which the source, gate and drain are formed within a trench in a semiconductor substrate. In this trench transistor, the gate width (where, as is understood in the art, the gate width is the dimension perpendicular to the flow of majority charge carriers through a conduction channel in the conduction channel accommodation portion and the gate length is the dimension parallel to the flow of majority charge carriers through the conduction channel) is determined by the depth of the trench and can be increased substantially without increasing the surface area occupied by the transistor, thereby enabling the device to have a good conduction channel width to length ratio and so a low on-resistance (Rdson) and good current handling capabilities or gain, without occupying an overly large area of semiconductor. However, the trench transistor proposed in U.S. Pat. No. 4,835,584 is not capable of withstanding high voltages between the source and drain regions when the device is non-conducting.
It is an aim of the present invention to provide a lateral field effect device having a trench gate structure which, in addition to having a low on-resistance, also has good reverse voltage withstanding characteristics.
In one aspect, the present invention provides a semiconductor device as set out in claim 1.
In one aspect, the present invention provides a lateral field effect device having a gate structure extending within a trench which is elongate in a direction between source and drain regions of the field effect device and wherein the trench extends from the source region and terminates in a voltage sustaining zone consisting of first regions of one conductivity type interposed with second regions of the opposite conductivity type with the dopant concentration and the dimensions of the first and second regions being such that, when the zone is depleted of free charge carriers in a mode of operation, the space charge per unit area in the first and second regions balances at least to the extent that the electric field resulting from the space charge is less than the critical field strength at which avalanche breakdown would occur. The gate structure may be an insulated gate structure and a plurality of parallel elongate trenches each containing an insulated gate structure may be provided. In an embodiment, the interposed first and second regions are elongate in a direction parallel to the direction in which the trench is elongate.
In one aspect, the present invention provides a semiconductor device comprising a semiconductor body comprising a field effect device, the semiconductor body having source and drain regions spaced apart in a first direction by a body region and both meeting a surface of the semiconductor body, the field effect device having a plurality of gate structures extending parallel to one another in a second direction perpendicular to said first direction in respective trenches for controlling a conduction channel in conduction channel accommodation portions of the body region extending along at least side walls of the trenches, each gate structure being elongate in said first direction and having first and second ends with the first end being surrounded by the source region, the field effect device having a voltage sustaining zone comprising first regions of one conductivity type interposed with second regions of the opposite conductivity type with the dopant concentrations and dimensions of the first and second regions being such that, when the zone is depleted of free charge carriers in a mode of operation, the space charge per unit area in the first and second regions balances at least to the extent that the electric field resulting from the space charge is less than the critical field strength at which avalanche breakdown would occur, each of the first and second regions being elongate in said first direction such that each first region extends between a conduction channel accommodation portion and the drain region and each second region extends between a portion of the body region spaced from the conduction channel accommodation portions and the drain region.
In one aspect, the present invention provides a semiconductor device comprising a semiconductor body comprising a field effect device, the semiconductor body having source and drain regions spaced apart in a first direction by a body region and both meeting a surface of the semiconductor body, the field effect device having a plurality of gate structures extending parallel to one another in a second direction perpendicular to said first direction for controlling a conduction channel in conduction channel accommodation portions of the body region each gate structure being elongate in said first direction and having first and second ends with the first end adjoining the source region, the field effect device having a voltage sustaining zone comprising first regions of one conductivity type interposed with second regions of the opposite conductivity type with the dopant concentrations and dimensions of the first and second regions being such that, when the zone is depleted of free charge carriers in a mode of operation, the space charge per unit area in the first and second regions balances at least to the extent that the electric field resulting from the space charge is less than the critical field strength at which avalanche breakdown would occur, each of the first and second regions being elongate in said first direction such that each first region extends between a conduction channel accommodation portion and the drain region and each second region extends between a portion of the body region spaced from the conduction channel accommodation portions and the drain region.
In an embodiment the gate structures are insulated gate structures.
A semiconductor device embodying the invention enables a lateral trench field effect device to be provided that has good current carrying capabilities and low on-resistance whilst also enabling relatively high voltages between the source and drain region to be withstood when the field effect device is non-conducting.
It should be noted that U.S. Pat. No. 4,754,310 (our reference PHB32740) describes a semiconductor device having a voltage sustaining zone formed of first regions of one conductivity type interposed with second regions of the opposite conductivity type with the dopant concentrations and dimensions of the first and second regions being such that, in a mode of operation when the zone is depleted of free charge carriers, the space charge per unit area in the first and second regions balances at least to the extent that the electric field resulting from the space charge is less than the critical field strength at which avalanche breakdown would occur.
Other advantageous technical features in accordance with the present invention are set out in the appended dependent claims.